Car and Recycling

Latest Advanced Technology and Tasks in Automobile Engineering

Seminar 12: Cars and Recycling

Jenna M. Eason

Current state of recycling of scrap aluminum and the recycling technologies.

In 2005 North America’s passenger cars contained an average of 170kg of aluminum [2].  With this number growing, it is necessary to find new developments in recycling technologies in order to decrease wastes.

US Patent: 4282044

Method of Recycling Aluminum Scarp into Sheet Metal for Aluminum Containers. [1]

This patent describes a method where scrap (including consumer, plant, and can) is melted in a heated furnace with minimum adjustment to create an alloy composition of silicon, iron, manganese, magnesium, copper and titanium.  The composition is then cast and fabricated into sheets with strength and formability properties, which make it suitable for container manufacture.  The sheet fabrication includes direct chill casting, scalping, preheating, hot breakdown rolling, continuous hot rolling, annealling, cold rolling, and shearing.  The sheet manufacture may be drawn-and-ironed, easy-opening, continuous strip casting, and/or solution heat treatment.

Recycling Light Metals from End-of-Life Vehicles [2]

Using aluminum drastically reduces weight, which translates into improved fuel economy and reduced greenhouse gas and polluting emissions, while offering the same or better stiffness and crashworthiness.  However, using a recycled aluminum can reduce energy required to produce.  Remelting of recycled metal saves almost 95% of the energy needed to produce prime aluminum from ore, and, thus triggers associated reductions in pollution and greenhouse emissions from mining, ore refining, and melting.  Already in 2001, more than half the aluminum content in cars and light trucks is from recycled material. 

The metal recycling system in North America (2001) includes approximately 6000 scrap collection and dismantling yards, 200 scrapshredders, ten sink-float plants and – one sole metal sorter separating wrought from cast aluminum.  An ELV traveling through this system is first dismantled for parts for reuse and rebuild.  Parts that are not in demand retain on the hulk, which is flattened and bailed with other hulks for reduction of transportation costs to the scrap shredder.  The entire hulk then has its 45 seconds in the shredder, where it is reduced to 0.10 diameter.  The pieces then undergo a variety of separation processes for material recovery at the shredder facility and are magnetically separated, then separated by air suction.  What is left is NMSF.  That concentrate is sold for farther separation at sink-float plants (separated by specific gravity).  Aluminum particles are present in both of the larger separations.  Metal particles are separated again from non-metallics by ECS, yielding a mixed-alloy aluminum product and an aluminum-magnesium mix.

The aluminum industry must work with alloys designated for high recycled content to further improve metal-treatment methods, forming and fabrication processes to match the formability and product properties of the current prime-sourced products, and, if possible, to further relax the limits on the content of impurity elements in these alloys.  Current developments include tinting the sheet/extrusion aluminum using an Alcoa-patented etching process and color-sorting the aluminum into tighter family groupings, and chemically analyzing each shred particle and piece-by-piece batch automotive aluminum sheet/extrusion alloys from the analyzed shred- a technology that also has promising future applications in the separation of MgAlZn alloys from MgAlMn alloys in batching magnesium-alloy compositions.

One goal is to be able to take scrap metal from one market segment (building demolition, shredded machinery, etc.) and use it in another for long-term sustainability and best economics of the overall light-metal recycling system.  The challenge for the recycling industry will be to industrially implement the new recycling technologies fast enough to match the growing flow of light-metal scrap from ELV. 

Sources:

1) United States Patent: 4282044: Method of Recycling Aluminum Scarp into Sheet Metal for Aluminum Containers.

2) Gesing, A., and Wolanski, R., “Recycling Light Materials from End-of-Life Vehicles”, pp. 21-23, November 2001